(1) Field of the Invention
The present invention relates to an adhesive composition having a high bonding force and an excellent durability. More particularly, the present invention relates to an adhesive composition especially valuable as a dental adhesive.
(2) Description of the Related Art
A variety of adhesive are used in various fields, and recently, they are extensively used in the automobile industry, the electric power industry and related industries, the construction field and the medical industry. Adhesives having excellent properties required in the respective fields have been developed. Adhesives used in the medical field, for example, dental adhesives used for restoration of teeth, are required to have strong bonding force and high durability sufficient to resist severe conditions such as those in the oral cavity. Accordingly, various dental adhesives having special functions capable of resisting severe conditions have been proposed.
For example, Japanese Pat. No. 33363/81 proposes an adhesive composition comprising an acrylic acid ester type vinyl monomer, an organic peroxide, and amine and a sulfinic acid salt. In this adhesive composition, it is intended to increase the bonding strength by using a ternary curing system comprising an organic peroxide, an amine and a sulfinic acid salt. Indeed, according to this proposal, a certain improvement over the conventional adhesive compositions can be attained. However, the adhesiveness to the dentine of a tooth is still insufficient, and it is necessary that the bonding force to the enamel of a tooth or a metal should be increased.
Japanese Patent Publication No. 36791/79 proposes a dental adhesive composition comprising an acrylic acid ester type vinyl monomer, an organic peroxide, an amine and an L-ascorbic acid. The object of this proposal is to adjust the curing time of the dental adhesive composition, and it is taught that this composition is advantageous in that an appropriate operation time can be obtained by using an L-ascorbic acid as the co-catalyst. However, from the results of tracing experiments made by us, it was confirmed that increase of the bonding force cannot be expected, though the curing time can be effectively adjusted.
Furthermore, Japanese Patent Publication No. 17513/83 and Japanese Patent Publication No. 30681/84 propose an adhesive comprising an acid group-containing monomer such as 4-methacryloxyethyltrimellitic acid and/or an anhydride thereof, a vinyl compound and a radical initiator. In this adhesive composition, if tri-n-butylborane oxide is used as a catalyst, the bonding force to the dentine of a tooth can be improved, but since tri-n-butylborane oxide reacts with oxygen in air and ignition is caused or the oxide is rendered inactive, scrupulous care is necessary for the handling. Moreover, the improvement of the adhesion strength is still insufficient.
Therefore, development of an adhesive composition having sufficient bonding force and durability even in a special environment, for example, a dental adhesive having such excellent characteristics in the oral cavity, is eagerly desired in the art.